In spark-depositing techniques, an electrode typically serves as a source of the substance to be deposited on the workpiece surface. As a localized portion of the electrode and a localized portion of the workpiece surface are brought into and/or out of mutual contact, spark discharge is caused to develop between them with a brief electrical impulse which is of an intensity sufficient to produce fusion of the localized electrode portion so that the localized fusion substance in a small amount is transferred to the small localized discharge-impinging area of the workpiece and cooled thereon to form a firm metallurgical bond with the workpiece substrate. By continuous sweeping such contact discharge over a selected surface region of the workpiece, a uniform layer of the deposit substance which is effective to harden or otherwise modify the original surface can be obtained.
In a typical form of spark-deposition, the electrode may be a solid rotary member rotated to bring its end face in sliding or tangential movement over the workpiece surface and the electrode substance is transferred onto the latter with the aid of repeated contact discharges. Such intermittent contact discharges can be effected by a capacitor circuit designed to charge and instantaneously discharge across the points of contact between the electrode and the workpiece and recharge as the contact regions shifts from one contact to a next contact point between the electrode and the workpiece. Otherwise, a mechanical or electrical switching of a continuous voltage source has been employed to provide periodically a pulsed voltage across the moving interface of the electrode and the workpiece.
An electrode member composed of the depositable substance may also be repeatedly driven into contact with a workpiece, for example, under a spring force applied to the electrode held resiliently upon an electrode holder. A spark discharge is drawn between the electrode tip and the workpiece from a charged capacitor, thereby creating a partial weld between them. Coupled with the electrode holder, there is an electromagnetic coil designed to be energized at least in part by the charging current of the capacitor or short-circuit condition between the electrode and the workpiece. The coil is thus operable, upon the capacitor discharge, to draw the electrode tip abruptly away from the workpiece surface in order to break the weld and leave substance from the electrode tip deposited upon the workpiece.
With whichever rotary and vibratory systems described is employed, it has so far been commonly believed that spark-depositing operations are relatively laborious and inefficient tasks inasmuch as the operator needs to manipulate the electrode assembly and to renew the consumed electrodes from time to time. Thus, the problems particularly arise where a large workpiece and a number of workpieces should be coated by spark-deposition, necessitating a large amount of the depositable substance to be furnished by the spark-depositing electrodes.